Ask an Expert: What Influences the Strength of the Northern Lights?

The magical beauty of the northern lights draws lots of people to Iceland. In fact, a whole lot of people plan their entire trips around the forecasted activity. So when are the Aurora Borealis at their strongest? And what, if anything, influences their activity? We went to Marcel de Vries, a meteorologist at the Icelandic Met Office, for answers.

“The northern lights are a result of solar activity hitting the geomagnetic field of the earth, which guides the material being shot out from the sun towards the poles of the Earth. That’s the reason why you can see them in polar areas and not, for example, near the equator,” Marcel explains.

Put simply, the surface of the sun can be an unruly place, with solar winds and explosions spitting out particles in all directions at very high speeds. If the direction is Earth, then those solar particles enter the upper atmosphere (meaning several hundred kilometres from Earth’s surface) and collide with the molecules there.

“The sun particles collide with those molecules, creating energy, releasing it as light. So, for example the green lights come from (ionised) nitrogen atoms and sometimes you have pinkish-red lights, which are more from oxygen atoms,” according to Marcel. Things like altitude, particle energy and light wavelength also factor into the colours we see in the sky.

The amount of solar activity also depends on the solar cycle — the 11-year intervals at which the sun’s magnetic field flip. That cycle can be observed by monitoring the rising and then falling activity on the sun, mainly through occurrences of sunspots. On satellite pictures they show up as dark spots on the solar surface, with more spots meaning more activity.

Marcel points out that sunspots are relatively cool (in the temperature sense) regions of instability, with explosions on the sun mostly happening around them, spewing a lot of material into space. Currently the sun is on an upward curve of activity, reaching its max in 2025 and promising a continued uptick in northern lights in the meantime.

Even with increased solar activity, we’d advise against putting all your hopes and dreams into epic Aurora sightings if you’re visiting Iceland for a finite amount of time. The weather and a bunch of other factors will also play a part in whether or not the lights will be visible on any given night.

“There are a lot of myths around the northern lights,” Marcel points out. “A lot of people say that it needs to be very cold for northern light activity and that’s not true in a scientific sense, but it is in a more practical way. In order to see the northern lights, it needs to be very clear, without any clouds, and usually if you look at weather patterns, the best chance to have a cloudless sky, especially here in the south-west, is when you have a cold wind from the north. There may also be a lot of northern lights activity when it’s cloudy — you just won’t see it.”

Read more of the Grapevine’s Ask An Expert series here.